Protection of Transformers against Surge Voltage

Authors: Anil S. Khopkar, Umesh N. Soni

Abstract:

Surge voltage arises in the system either by switching operations of heavy load or by natural lightning. Surge voltages cause significant failure of power system equipment if adequate protection not provided. The surge arrestor is device which is connected in a power system to protect the equipment against surge voltages. To protect the transformers against surge voltages, metal oxide surge arrestors (MOSA) are connected across each terminal. The Basic Insulation Level (BIL) of transformers has been defined in the national and international standards based on its voltage rating. While designing transformer insulation, factors such as BIL, surge arrestor ratings, and its operating voltage have to be considered. However, the performance of transformer insulation largely depends on the ratings of the surge arrestor ratings, their location, the margin considered in insulation design, the quantity of surge voltage strikes, etc. This paper demonstrates the role of surge arrestors in protecting transformers against overvoltage, transformer insulation design, the optimum location of surge arrestors and their connection lead length, insulation coordination for transformers, the protection margin in BIL, and methods of safeguarding transformers against surge voltages in detail.  

Keywords: Surge voltage, surge arrestors, transformer, protection margin.

References:

[1] IEC:60071-2-2023, “Insulation Co-ordination – Application Guidelines”.
[2] IEEE Guide for the Application of Metal-Oxide Surge Arrestors for Alternating-Current Systems”- 2013.
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[5] Saad Abdul Basit, Chokri Belhaj Ahmed, Firoz Ahmad1 and Mohammed Arif “Lightning Overvoltage Analysis of a 380 kV Gas Insulated Substation Using PSCAD/EMTDC”,2020 2nd International Conference on Smart Power & Internet Energy Systems.
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[7] IEC:60099-5-2013, “Selection and application recommendations”.